The Internet Protocol (“IP”) and Transmission Control Protocol (“TCP”) are rapidly becoming the lingua franca of modern data networks. Currently, host protocol stacks allow a single host to support multiple physical and logical data-link interfaces.
These interfaces may be either software or a combination of hardware and software. A data-link interface is typically a device that permits a host to communicate with another entity. Data-link interfaces may be active for as long as the host is running, or they may activate and de-activate dynamically. An example of a data-link interface is an Ethernet interface which consists of the Ethernet card along with a device driver. Typically the Ethernet interface becomes active upon system boot and remains active until the host computer is shut off.
Data-link interfaces typically represent an IP address that is bound to a data-link device. Communication via these interfaces occurs through device-independent calls to a socket application programming interface (“API”). As is known in the art, a socket is an endpoint, in a host computer's protocol stack, for communicating over a data network. The socket API provides the capability for application programs and their processes to access communications protocols automatically. The socket API exists logically above a transport layer for the TCP/IP stack, but below an application layer. The socket API, which is well known to those skilled in the art, is discussed in UNIX on-line manuals as well as many textbooks.
At present, all processes typically bind to one common IP address. When a process initiates an IP communication, the protocol stack binds the common IP address to the process. In this sense, all processes typically communicate over the same IP interface. Data traffic to or from one application is typically distinguished from data traffic to or from another application by a transport-layer parameter such as a TCP or User Datagram Protocol (“UDP”) port. For some processes, however, having one common IP address may be restrictive.
Currently, protocol stacks may support multiple IP interfaces in a limited sense. A host with more than one physical interface may require more than one IP address. For example, a host computer may communicate using IP packets over a Point-to-point Protocol (“PPP”) connection via a modem while simultaneously communicating using IP packets over an Ethernet connection. In this case, the Ethernet interface and the PPP interface would be associated with separate IP addresses. The processes on the host computer, however, have these separate IP addresses in common. Any process that communicates over the modem does so using the common IP address for the PPP connection. Similarly, any process that communicates over the Ethernet connection does so using the common IP address for the Ethernet connection.
Future communication systems, however, may require that a protocol stack is capable of supporting multiple IP addresses in a broader sense: different processes on the same host are associated with different IP addresses on the same physical interface. Processes may request a new IP interface with a new IP address rather than share a single IP address with all other processes. Instead of distinguishing traffic to and from processes by port numbers, the traffic may be distinguished by IP address.
It is therefore desirable to provide a method for binding multiple IP addresses to the same process. Multiple processes on the same host may then be assigned different IP addresses that are distinguishable at an application layer.